The hoof walls aren’t finished yet. Look again to the sole. You’ll probably see it craving a slightly shorter hoof wall at the quarters (the sides of the hoof wall, between the back of the toe and the heels).
This is the natural direction of the hoof. The slight arch (or ‘scoop’ as it’s called) helps the hoof expand on impact. It’s a vital component of the horse’s shock absorbing system.
As with a shod horse, quarters that are the same length as the toe result in a flat foot. The hoof cannot expand, and unwelcome stresses surround the hoof wall. ‘Bulging’ higher up, is a common occurrence where quarters are left too long.
Use flat ground, or a rasp to check along the sides of the hoof. The scoop shouldn’t be too prominent (only 2-3mm) – just enough room to tuck your fingernail underneath. And the arch should remain just above the level of sole.
Though small, the scoop must exist for healthy hoof function. If needed, trim a slight arch into the sides of the hoof wall, and inspect again on a flat surface.